i6 DISEASES OF TREES 



from parents to descendants ; at least nothing is known so far 

 that indicates such an inheritance. This holds good not only 

 for the causes but also for the diseases themselves. 



A transmission, by inheritance, of diseases to descendants is 

 unknown in the vegetable kingdom. One may without hesita- 

 tion make use of the seeds of plants suffering from any con- 

 ceivable disease for the propagation of new plants. In par- 

 ticular one may without scruple collect the seed of such trees as 

 are dwarfed owing to poverty of the soil. Indeed, as a matter 

 of fact, this is done, for instance, in the case of the Scotch 

 pine, the cones of which are gathered by preference from those 

 trees whose proportions are so diminutive, owing to their grow- 

 ing on barren moors, that the collection of the cones may be 

 accomplished with ease without climbing the trees. It is only 

 when a question of individual properties consisting in dwarfed 

 habit of growth, spiral stems, or other undesirable peculiarities 

 that are innate in the plant is involved, that the law of in- 

 heritance comes into consideration, and then propagators of 

 plants have to exercise the greatest care. 



METHOD OF PROCEDURE IN INVESTIGATING THE 

 DISEASES OF PLANTS 



Reference will here shortly be made to the methods of investi- 

 gation which we have to follow when we wish to determine the 

 causes of diseases in plants. 



In the case of diseases of men or animals the difficulties of 

 diagnosis are much increased by the fact that in the great 

 majority of cases the disease of a single organ or part of the 

 body is followed by secondary phenomena which impede the 

 discovery of the proper seat of disease. In the bodies of plants, 

 where the nervous system is absent, a disease as a rule remains 

 localized, at least at first. The division of labour is not yet so 

 far differentiated as in the bodies of the more highly organised 

 animals, where disease of any organ, often even a small one, 

 involves the whole body sympathetically. A large part of the 

 body of a plant may be diseased and even killed without the 

 plant being necessarily perceptibly injured in its general health. 

 If we have succeeded in observing the disease in its first stage, 



